A cataract is a cloudiness or opacity which develops in the lens of the eye which is normally clear and transparent. A person with impaired vision due to a cataract may have his vision improved through a combination of cataract surgery and proper corrective lenses.
An ophthalmologic surgeon may elect one of several different surgical procedures for removing a lens that has a cataract. Intracapsular cataract extraction is a technique for the removal of the entire cataract, including its capsule, in one piece. Extracapsular cataract extraction and phacoemulsification and aspiration are two surgical technique that involve the removal of the opacified portions of the lens, while the clear posterior capsule which was the original support for the lens is left in place.
Intracapsular or extracapsular extraction eliminates the cloudiness or opacity caused by the cataract, but light entering the eye is now unfocused since the lens has been removed. Light entering the eye may be focused by an intraocular lens.
Ophthalmologic surgeons now generally recognize that it is better optically an physiologically to implant the intraocular lens into the posterior chamber of the eye. Intraocular lens implants have also been done in the anterior chamber in which the lens is implanted forward of or mounted to the iris. Implantation of the intraocular lens behind the pupil has been found to cause fewer secondary problems following extracapsular surgery, particularly glaucoma and swelling of the eye called cystoid macular edema.
Intraocular lens implants into the posterior chamber also have been found to have some secondary complications. Nearly half of the patients who have had extracapsular cataract extraction experience some loss of visual function from clouding of the posterior capsule within several months to several years after the initial surgery. In order to restore a patient's visual function, further surgery becomes necessary to make an opening in the posterior capsule with a knife or a laser.
Ophthalmologic surgeons in the past have tried to design intraocular lenses for implant into the posterior chamber that retard the opacification or clouding of the posterior capsule membrane left following the extracapsular cataract extraction. One of the first intraocular posterior chamber lenses designed to retard opacification and to facilitate discission of the membrane is diclosed in U.S. Pat. No. Re. 31,626, issued on July 10, 1984 to Kenneth J. Hoffer. Hoffer designed a lens having a convex-plano relationship where the power is put in the front or anterior surface of the lens. The rear or posterior surface has a ridge intended to prevent the lens cells from sliding in beneath the ridge, thus retarding opacification. The Hoffer lens had an opening along the circumferencial ridge for insertion of a surgical knife or needle through the opening in the posterior chamber in the space behind the lens, but there is no contact of the lens optic with the posterior capsular membrane.
Another design for an intraocular posterior chamber lens is disclosed in U.S. Pat. No. 4,485,499, issuing to Lawrence D. Castleman. The lens has a convex front face and a generally planar rear face with two parallel projecting members. The projecting members were said to provide a separation or open zone at the visual axis between the lens body and posterior capsule to facilitate corrective discission surgery. Again, this lens does not provide contact of the lens optic with the posterior capsular membrane (PCM).
Yet another design of a posterior intraocular lens is disclosed in U.S. Pat. No. Re. 31,998, reissued on Oct. 8, 1975 to William D. Myers. The Myers lens implant was intended to facilitate laser posterior capsulotomy following extracapsular surgery. In one form, the lens has a front convex surface, and a bridge spaces the generally planar rear surface of the optic forward of the posterior capsule. In a second form, the lens has a convex front surface, but the rear surface optic is concave to provide a space forward of the posterior capsule. This lens also does not provide lens optic contact with the PCM.
It is therefore an object of the present invention to provide an improved intraocular posterior chamber lens that overcomes disadvantages of prior art lenses in retarding opacification following extracapsular cataract extraction and reducing the likelihood of secondary surgical procedures.
It is another object of the invention to provide an improved intraocular posterior chamber lens having a convex rear surface with a constant radius of curvature in direct apposition with the posterior capsule of the eye to improve early visual acuity following cataract extraction and to retard opacification in an area of direct contact of the optic with the PCM.
It is another object of the invention to provide an intraocular posterior chamber lens in which the optic power modification for the lens is achieved by the modification of the anterior or front side of the lens. This will effect less contact of the anterior surface of the intraocular lens implant with the iris, which is a frequent clinical occurence with the above referenced designs.
It is still another object of the invention to provide an improved intraocular posterior chamber lens in which an annular space is provided beneath the lens body and outside the optic zone of the lens implant to facilitate YAG laser surgery or knife discission, which may be required as a secondary surgical procedure sometime after implantation of the intraocular lens.
It is still another object of the invention to provide an improved intraocular posterior chamber lens having an optic and haptic design enabling manufacture of a foldable soft intraocular lens suitable for surgical injection through a small incision into the eye.